Set a "kernbase" symbol in 32-bit arm locore.S and use it with ldscript.arm.

This brings arm into line with how every other arch does it.  For some
reason, only arm lacked a definition of a symbol named kernbase in its
locore.S file(s) for use in its ldscript.arm file.  Needlessly different
means harder to maintain.

Using a common symbol name also eases work in progress on a script to help
generate arm and arm64 kernels packaged in various ways (like with a header
blob needed for a bootloader prepended to the kernel file).

sys/arm/arm/locore-v4.S

@@ -62,9 +62,11 @@ __FBSDID("$FreeBSD$");
  */
 	.text
 	.align	2
+
+	.globl kernbase
+	.set kernbase,KERNVIRTADDR
+
 #ifdef PHYSADDR
-.globl kernbase
-.set kernbase,KERNBASE
 .globl physaddr
 .set physaddr,PHYSADDR
 #endif

sys/arm/arm/locore-v6.S

@@ -59,6 +59,9 @@ __FBSDID("$FreeBSD$");
 	.text
 	.align	2
 
+	.globl kernbase
+	.set kernbase,KERNVIRTADDR
+
 #if __ARM_ARCH >= 7
 #define	HANDLE_HYP							\
 	/* Leave HYP mode */						;\

sys/conf/Makefile.arm

@@ -61,7 +61,7 @@ KERNVIRTADDR= 0xc0000000
 # "ELF for the ARM architecture" for more info on the mapping symbols.
 SYSTEM_LD= \
 	${SYSTEM_LD_BASECMD} \
-	    --defsym='text_start=${KERNVIRTADDR} + SIZEOF_HEADERS' \
+	    --defsym='text_start=kernbase + SIZEOF_HEADERS' \
 	    -o ${.TARGET} ${SYSTEM_OBJS} vers.o; \
 	$(OBJCOPY) \
 	    --wildcard \
@@ -77,7 +77,7 @@ KERNEL_EXTRA_INSTALL+= ${KERNEL_KO}.bin
 ${KERNEL_KO}.bin: ${SYSTEM_DEP} vers.o
 	@echo "linking ${.TARGET}"
 	@${SYSTEM_LD_BASECMD} \
-	    --defsym='text_start=${KERNVIRTADDR}' \
+	    --defsym='text_start=kernbase' \
 	    -o ${.TARGET} ${SYSTEM_OBJS} vers.o
 	${SIZE} ${.TARGET}
 	@${OBJCOPY} \